DESCRIPTION: The primary auditory cortex in the adult is physiologically plastic, rather than static as has been traditionally assumed. Behavioral learning produces shifts of the frequency tuning of auditory cortical neurons toward or to the frequency of an acquired behaviorally important sound. Learning-induced plasticity is due to associative processes rather than arousal or attention, is highly specific to the important frequency, is rapidly acquired and lasts indefinitely, as tested for months. Therefore, the basic processing of acoustic frequency is not simply determined by the physical parameters of sound but also by its acquired behavioral importance. Understanding the highest level of the auditory system depends upon understanding how learning modifies auditory information processing. The goal of this project is to initiate the solution of this problem. Specifically, it will determine the effects of learninbg on fundmanetal parameters of response to acoustic frequency: Characteristic frequency (CF), threshold level of the CF (Th) and bandwidth or response at levels above threshold (BW). These parameters provide sensitive measures of information processing -- CF indexes tuning; Th indexes sensitivity; BW indexes selectivity. This will be accomplished by determiing in adult behaving guinea pigs, the response areas (frequency by intensity) of neighboring single neurons before and at various intervals after different types of behavioral training: habituation, sensitization, classical conditioning,instrumental conditioning. Additionally, the rate of development of learning-induced plasticity will be determined. This project will help explain learning effects in the normal human. Moreover, it has significance for understanding the learning that occurs in pathologies and therapies, such as learning to perceive speech following cochlear implants and for recently identified learning-based remediation of acoustic processing deficits in dyslexia.